On June 4, 2011, Puyehue-Cordón Caulle in Chile experienced its first major eruption in decades. The volcano sent an ash plume eastward, disrupting air traffic, threatening water supplies, and even dropping golf ball-sized pumice on parts of Argentina. From the start, the volcanic plume towered over local clouds.

The top image is a nighttime scene acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite. This false-color image is made from observations of infrared light. The image is rotated and north is at right.

Running across the MODIS image is a yellow line that corresponds to the vertical profile of the atmosphere shown in the graph below. The atmospheric profile was acquired by Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), a joint mission between NASA and the French Centre National d’Etudes Spatiales (CNES). CALIPSO carries a laser (lidar) that sends quick pulses of light through the atmosphere and a receiver that detects the returning light that bounces off clouds and atmospheric particles. The strength of the returning signal illuminates characteristics of the clouds or particles.

In the lidar profile, the volcanic plume rises well above the clouds to the north—roughly 15 kilometers (9 miles) high. At mid-latitudes, the bottom of the Earth’s stratosphere begins around 10 kilometers (6 miles) above the surface. Stratospheric winds have a strong tendency to carry material eastward, so volcanic ash from this eruption may travel great distances, disrupting air traffic as it goes.

Volcanic ash is very different from ash from ordinary fires, which is soft and fluffy. Volcanic ash is made of tiny, jagged particles of rock and glass that are very abrasive and slightly corrosive, and can even conduct electricity when wet. Volcanic ash can irritate respiratory systems, coat vegetation and leave it inedible to wildlife and livestock, and destroy machinery. By working its way into airplane engines, volcanic ash can take down planes in mid-flight.

Because of the hazards volcanic ash poses to airplanes, eruptions frequently cause delays and diversions to air traffic. The Puyehue-Cordón Caulle eruption was no exception. Argentinean air traffic has been hampered, and by June 13, 2011, the ash had spread as far away as Australia and New Zealand, according to news reports.